The mollusc Aplysia, and a number of other invertebrates, have proven extremely useful in studies of basic cellular neurobiology. In large part this is because of the extraordinarily large size of its nervous system cells (some of which are almost a millimeter in diameter) and the ability to recognize these cells as unique individuals. This has allowed the investigation of individual cells, their patterns of interconnections, modulation of synaptic strength, behavior, learning and development. In 1988, Cold Spring Harbor sponsored the first meeting devoted to work on the opisthobranch mollusc Aplysia. Because of the success of this meeting, we decided to convene at two- to three-year intervals at the Cold Spring Harbor Laboratory and alternate there with the highly successful Drosophila neurobiology meeting. The third meeting in April, 1993, drew over one hundred and twenty participants, and again was highly successful. The proposed 1995 meeting will continue to provide a format for discussing new methods and findings that have emerged in the cell and molecular biology of Aplysia and other model invertebrate systems. These findings will be considered in eight different sessions, each concerned with a different level of analysis: ion channels and channel modulation; peptides and small molecule transmitters; synaptic transmission cell imaging; circadian rhythm; neuronal circuitry and behavior; learning; development. One important change from the previous meeting is that, in many of the sessions, we now plan to invite one or two speakers who work with model invertebrate systems other than Aplysia. We expect about 150 participants from approximately 60 laboratories throughout the world.